MUTE note working on DirectTV Stream remote

Has it ever worked?

We had the Dish DirectTV and switched to the Stream Direct TV about 10 days ago.  The volume and the mute button did not work so we went back to the AT and T store and spoke with the sales person that sold the streaming equipment to us.  He came to our home and fixed the volume issue but could not figure out why the MUTE would not work.  We have surround sound Dolby and he thinks this may be the iissue.  I have searched the Internet to find out how to resolve the issue but cannot find any information.